In what sense do they not fit? Or rather, let me put it this way: I know from experience that it isn't particularly complex to attach nearly any sort of light to that sort of box, including lights from IKEA. Typically you'd only need a screwdriver and drill sufficient to make holes for anchoring. In more extreme cases you'd want a spool of wire, nippers, and line or two of terminal connectors, also all available from the standard home improvement places.

All that said, "Electrical Work for Beginners" isn't a course I'd want the responsibility for teaching, much less over an internet forum. It may not be particularly complex, but the cost of failure can be high. So the more you ask, the more strongly I find myself agreeing with the suggestion that you buy whatever you want and then pay for an hour or two of electrician's time to get them fit.